Shrinkage of web material such as paper



Nov. 11, 1969 RABSTAD 3,477,906

SHRINKAGE 0F WEB MATERIAL SUCH AS PAPER Filed March 9, 1966 INVENTOR L423 P053 7790 ATTORNEY United States Patent O 3,477,906 SHRINKAGE F WEB MATERIAL SUCH AS PAPER Lars Rabstad, Moss, Norway, assignor to M. Peterson & Son A/S, Moss, Norway, 2: company of Norway Filed Mar. 9, 1966, Ser. No. 532,839 Int. Cl. D21f 11/00; D21h /06, 5/24 US. Cl. 162-205 4 Claims ABSTRACT OF THE DISCLOSURE This present invention relates to the operation of a socalled shrinkage presses, by means of which web material, particularly paper, is treated in order to acquire a better extensibility. More specifically the invention relates to presses, in which the web material is passed through a press nip where an elastic layer is pressed against a hard heated surface running at a slightly different speed.

In the operation of such shrinkage presses, difficulties arise on account of the necessity of having the width of the paper web coincide with the axial length of the press nip, as the edges of paper will not be treated if they extend beyond the press nip, and the winding up of the paper gets difiicult. On the other hand, if the width of therunning paper web is so small that the web does not fill out the press nip completely up to the two opposite ends thereof, direct contact is obtained between the hard heated roll surface and the elastic layer which causes, among other things, that the latter is rapidly worn out.

The object of the invention is to eliminate said diff ficulty so that it is not necessary to see to it very carefully that the paper web runs exactly correctly, and nevertheless a long life of the elastic layer can be ex pected. According to the present invention said object is realised in that a lubricant is supplied to those places of the press nip where the elastic layer is not held separated by the treated Web material from the roll surface but is in direct contact therewith. When practising said measure the treated paper web may, without hesitation, be given a smaller width than the axial length of the pressure nip of the roll.

The invention, the working conditions of various presses in which the invention may be used, as well as details and some preferred lubricants will now be more fully described with reference to the accompanying drawings wherein:

FIGURE 1 is an end cross sectional view of apparatus utilizing the process for applying lubricant to prevent shrinkage of web material such as paper;

FIGURE 2 is a top plan elevation view of apparatus utilizing the process for lubricating to prevent shrinkage of web material such as paper.

In the shrinkage of a running paper web in accordance with a known method, the paper web 2 to be treated is caused to pass in a moist condition through a press nip 3 formed by two rolls, 4 and 6; one roll 4 is provided with a surface layer of an elastic and resilient material 3,477,906 Patented Nov. 11, 1969 8, preferably rubber, while the other roll 6 is made with a hard and smooth metallic surface 10. The rolls are connected mechanically or electrically in such fixed mutual relation that the hard roll is driven with a peripheral speed about 10 to 20 percent higher than that of the rubber-clad roll. The rolls are pressed against each other with a line pressure of up to 30 kgs, per cm. and thehard roll 6 is heated to between 50 to C. The rubber layer 8 which is deformed in the press nip 3, contracts on the exit side of the nip and due to the frictional engagement with the paper web 2 the latter is caused to take part in the contraction while sliding against the, hard roll 6 which rotates at higher speed. In this manner the web is shrunk in its longitudinal direction without noticeable craping so that the paper, after stabilization of its structure by drying acquires a higher degree of extensibility than untreated paper.

:It is diificult to guide the paper web so that its position always coincides with the press nip accurately. If the ,edges of the web would reach outside the press nip, which may be caused by a quite normal transverse movement of the web by a few centimeters, its edges will be untreated and therefore not shrunk in the longitudinal direction, but will take on a wavy or crinkled contour making it diflicult to wind up the web with the use of conventional equipment for that purpose. On the other hand, if the paper web is chosen so wide relatively to the length of the press nip that the edges thereof will always pass through the press nip, then at the ends 12 of the nip the rubber-clad roll 4 will be pressed directly against the more rapidly rotating heated hard roll 6. On account of the heavy friction against the hard roll and the heat transferred therefrom, the rubber layer will be subjected to heavy stresses requiring that the material used therefor has high wearing resistance, high heat permanence and low rate of decomposition in the surrounding atmosphere. If all said requirements cannot be satisfied, the wear between the rolls at the contact points will cause wear, and as lateral movements of the web are almost unavoidable, wrinkles will soon occur at the edges of the web. Therefore, the soft roll will have a comparatively short life and must be replaced, which involves work stops and costs.

By supplying a lubricant 14 to those points of the press nip where the treated paper web does not separate the surface of the elastic roll from that of the opposed hard roll, the wear is practically eliminated at the places where the rolls directly contact each other. Therefore, the paper web may very well be of a somewhat smaller width than the length of the common generatrix of the rolls and nevertheless a durable shrinkage press can be obtained without a too restricted choice of materials for the surface layers of the rolls rubbing against each other.

In order to obtain the best possible eifect of the lubrication, the lubricant should be chosen with regard to the particular requirements of this special case. Thus, for the lubricant there should preferable be chosen a substance which is able to form a lubricating film of such a high viscosity that said film is not broken through at the prevailing pressure, speed difference between the roll surfaces and temperature of the press nip, and which is of such chemical constitution that it does not cause swelling of the elastic layer nor corrosion of the metallic roll surface. Further, one should preferably choose a lubricant of such a high viscosity that the paper web is not able, or is able only with difiiculty, to carry along the same with it. If such a lubricant is used as will be taken up by the paper web, said lubricant should preferably not have any influence upon the character of the paper when used, as is the case e.g. with certain silicon oils which may impart such a low surface friction to kraft paper that pasting thereof is diflicult and bags manufactured thereof are hard to pile. Another condition which may decide the choice of lubricants in certain cases is, that the same should be unrestrictedly miscible with water and not have any detrimental influence upon the web forming in a paper making machine. Then it is possible to dissolve the edges trimmed off the shrunk paper and to use the pulp obtained therefrom for the forming of paper anew upon the wire of the paper making machine. Moreover, the lubricant should be inert, so that it does not cause chemical or physical reactions that change the dimensions of the roll surfaces after some time of use, nor otherwise change the desired qualities of the materials.

Among substances that satisfy the above-mentioned requirements at least partially, there may be mentioned soapy water which will do as lubricant if the speed is held low, e.g. 5 to 25 meters per minute, and the temperature of the warm roll is held at 80 C. at the most;

The difficulty of choosing a suitable lubricant for more exacting working conditions reacts upon the choice of material for the surface layer of the soft roll. Instead of natural rubber which in many cases is not sufficiently durable, other elastomers must be chosen, particularly high polymers which, either pure or in admixture with natural rubber and by various treatments and other additions, may be given the desired physical qualities, including ability to be lubricated during the prevailing conditions. Thus, it has proved that a neoprene-covered roll has a considerably longer life when lubricated with certain polar substances which are miscible with water. Such substances can be, for example, polyhydric alcohols, esters, aldehydes, amides, and so forth. Particularly suitable are compounds having a high boiling point and a high viscosity as well as a weak swelling influence upon the elastic material. The latter also involves that fillers in the elastic material should not be influenced either. Nor should the elastic properties of the rubber be changed. A lubricant which has proved highly satisfactory, is glycerin.

The lubricant may be supplied by letting it drip onto or by spraying it upon one roll or both rolls at the ends thereof that come into direct contact with each other.

The invention is applicable not only to a shrinking press of the kind mentioned above and known e.g. from the US. Patent No. 3,104,197, but also to a shrinking press similar to that shown in the US. Patent No. 2,624,245 and in which the elastic layer consists of an endless blanket running in a loop and pressed by means of a sustaining roll or any other sustaining member against a heated hard roll. Therein the above-mentioned difficulties will be noticed particularly in the instance that the paper web before entering the shrinkage press is divided up in the longitudinal direction in order to get an increased transverse shrinkage. By supplying lubricant to those parts of the press nip lying between the two parallelly running parts of the paper web and at their edges, the drawbacks of the blanket rubbing direct against the surface of the hard roll are eliminated.

I claim:

1. A continuous process of producing a web material having extensibility in a longitudinal direction comprising the steps of:

feeding a web material into :a press nip,

passing said web material through said press nip where an elastic surface is pressed against a hard surface roll running at a different speed than said elastic surface,

pressing said web material in said press nip, and

supplying glycerin to those points of said press nip where said Web material does not separate the surface of the elastic surface from that of the opposed hard surface roll.

2. A continuous process of producing a web material 25 having extensibility in a longitudinal direction as claimed in claim 1 wherein the glycerin is supplied by spraying.

3. A continuous process of producing a web material having extensibility in a longitudinal direction as claimed in claim 1 wherein the glycerin is supplied by drippng.

4. A continuous process of producing a web material having extensibility in a longitudinal direction as claimed in claim 1 wherein said web material is a paper web.

References Cited UNITED STATES PATENTS 3,011,545 12/1961 Welsh et a1. 162361 3,035,512 5/1962 Beachler 2618.6 X 3,122,469 2/1964 Freuler 162-361 X 3,329,562 7/1967 Schaefer 162-361 FOREIGN PATENTS 633,128 12/1961 Canada.

S. LEON BASI-IORE, Primary Examiner US. Cl. X.R. 

